Many kinds of devices employing electrophotographic systems of a laser printer, copier or facsimile apparatus are incorporated with a roller such as a film developing roller, an electrically charging roller, or a transcribing roller. One example of these rollers is shown in FIG. 24.
A roller 10 has a core body 21 and a cylindrical forming body 12 fabricated with a resin. A metal mold for forming the roller 10 has, as shown in for example FIG. 25, a cylindrical metal mold 13 and core supporting members 14 located at upper and lower both edges of the cylindrical metal mold 13 for supporting a core 21 inserted inside of the cylindrical metal mold 13 and sealing both edges of the cylindrical metal mold 13. The lower core supporting member 14 is defined with a resin injecting inlet 16 for injecting a resin material into a roller forming space 15, while the resin injecting inlet 16 is urged outside of the metal mold with a resin injecting nozzle 18 of a forming machine from a semi-circular nozzle touch portion 19, so that the resin material is introduced into the roller forming 15.
After completion of filling the resin into the metal mold, the resin in the roller forming space 15 is hot-set. Hot-setting the resin, the core supporting members 14 are removed upward and downward respectively along an axial direction from the cylindrical metal mold 13. Subsequently, the core body 21 is extruded from the cylindrical metal mold 13 to take out a formed product (roller) held within the cylindrical metal mold 13.
The core supporting member 14 is provided with concave parts 17 for supporting the core body 21 at edges 21a, and in order to make easy insertion of the edge 21a of the core supporting member 14 into the concave part 17 or taking variation within dimensional tolerance of the edge of the core body into consideration, spaces of 10 to 20μare provided between the concave part 17 and the core supporting member 14. So, if the resin is poured into the metal mold at high pressure or if a pressure in the mold is high when the resin is expanded at hot-setting, a defect is present that the resin leaks out of the metal mold from the spaces. The leaked resin is adhered to the edges 21a of the core body 21 or to an interior of the concave part 17 of the core supporting member 14, and it should be removed after formed products have been released from the mold.
In case the core body 21 used to the resin roller is, as shown in FIG. 25, differs an outer diameter in the center part of the core body 21 and an outer diameter in the edge part 21a of the core body 21, and the outer diameter in the center part of the core body 21 is larger than that of the edge part, a method is to attach sealing members 24 (for example, O-ring) to the core supporting member 14 so as to contact side faces of the center part of the core body 21 for preventing the resin leakage.
However, the core body 21 being different in the outer diameters in the center part and in the center part thereof has disadvantages of high processing cost and high material cost of the core body 21, and accordingly a cost of the core body 21 is expensive.
In order to lower the cost of the core body 21 and make thickness of an elastic layer large for aiming at reducing rubber elastic hardness of the formed body 12 (elastic layer), such a core body 21 is sometimes used which uses core body 21 being the same in the center part of the core body 21 and the outer diameter in the edge part 21a of the core body 21.
In this case, as illustrated in FIG. 26, used is the core supporting member 14 which is buried with sealing members 24 (for example, O-ring) opening in the concave part 17 thereof. But there is a defect that the sealing members 24 buried in the core supporting member 14 are broken while repeatedly attaching the core body 21 to the concave parts 17, so that an effect for avoiding the resin leakage is decreased.
Further, for adopting a structure of burying the sealing members in the core supporting member 14, taking strength of burying grooves into consideration, it is necessary to bury the sealing members in depth of around 0.5 to 1 mm from the side edge face of a resin formed product of the core supporting member 14. Therefore, until around 0.5 to 1 mm from the side edge face of the resin formed product of the core supporting member 14, the resin leakage cannot be stopped with the sealing members 24, and the resin leakage 30 by the amount thereof occurs.
When using the core body 21 which is the same in the outer diameter in the center part of the core body 21 and the outer diameter in the edge part 21a thereof, a problem is to shorten a life of the sealing member and cause the resin leakage in parts from a resin formed edge part to the sealing member.
Thus, it is indispensable to frequently exchange the sealing members owing to the short life thereof and remove the leakage resin at edge parts, and in turn a cost-up of the resin roller is invited.
Next, reference will be made to using methods of the roller by use of an example of the resin roller for a photographic film developing process, referring to FIG. 27.
In various kinds of devices of the electrophotographic system, there is a system known as a photographic film developing process for visualizing electrostatic latent images, which supplies a nonmagnetic unary developer 55 on an image carrier 51 of a photosensitive body 50 of carrying the electrostatic latent image, adhering said developer to the electrostatic latent image on the surface of the image carrier, and contacting a developing resin roller 10a to the image carrier 51.
Using the nonmagnetic unary developer 55, this system is cheap in comparison with a system supplying the magnetic developer by use of the conventional magnetic roller. In a case of using a magnetic binary developer, a carrier itself has a short life, for example, it must be periodically exchanged per 10000 or 20000 copies, taking trouble for exchanging the carrier. On the other hand, the above mentioned system does not have such a defect. Further, in a case of using the magnetic binary developer, since the magnetic developer itself contains a magnetic substance near a different color, it is technically difficult to make the magnetic developer a color toner, but since the resin roller of the invention is employed to the nonmagnetic developing system using the nonmagnetic developer, such a problem is absent.
Typical shapes of the resin roller are shown in FIGS. 28, 29 and 30. The resin roller 10a has a core body 21, a cylindrical resin layer 12a formed with a resin around the core body 21, and a surface layer 12b covering the periphery of the resin layer 12a. 
A method for the resin roller 10a to send the nonmagnetic unary developer, depends on an electrically absorbing force, and since a property necessary as the developing roller makes the developer frictional electrification between the developing surface and a regulating blade 52 for regulating a piling thickness of the developer on the surface of the developing roller, the developer is easily cracked owing to pressurization, and such a developing roller 10a is served which covers a soft resin layer 12a on the core body 21 for avoiding the developer from cracking.
The resin layer 12a is often exposed at the surface, but for controlling electric charging of the developer or transferring performance, it is provided on the surface with a thin surface layer 12b. 
Further, explanation will be made to a producing method of the resin roller 10a. 
At first, a metal mold 120 for forming the resin layer 12a of the resin roller 10a has, as shown in for example FIG. 31, a cylindrical metal mold 13 and the core supporting members 14, 14 located at upper and lower both edges of the cylindrical metal mold 13 for supporting a core 21 inserted inside of the cylindrical metal mold 13 and sealing both edges of the cylindrical metal mold 13. The lower core supporting member 14 is defined with a resin injecting inlet 16 for injecting a resin material into a roller forming space 15 formed within the cylindrical metal mold 13, while the resin injecting inlet 16 is urged outside of the metal mold with a resin injecting nozzle 18 of a forming machine from a semi-circular nozzle touch portion 19, so that the resin material is introduced into the roller forming space 15.
After completion of filling the resin into the metal mold 120, the whole of the mold 120 is heated to hot-set the resin in the roller forming space 15. Hot-setting the resin, the core supporting members 14, 14 are removed upward and downward respectively along the axial direction from the cylindrical metal mold 13. Subsequently, the core body 21 is extruded from the cylindrical metal mold 13 to take out a formed product (roller) 10b held within the cylindrical metal mold 13.
After that, the resin layer 12a of the roller main body 10b produced by the above forming method is coated on the peripheral surface thereof with a treated liquid mixed with a resin material through a spray method, a dipping method or a roll coater method, and dried to form a surface layer 12b. 
The roller main body 10b produced by the above forming method has swelling parts at edge parts of the resin layer 12a as shown in FIG. 32 when releasing from the metal mold. A mechanism of the swelling phenomenon at the edge is explained that the swelling is generated by thermal expansion and shrinkage owing to temperature difference between temperatures at pouring the resin into the metal mold 120 and after releasing from the mold, the amount of shrinkage in the axial direction is larger than that in the peripheral direction, and the formed resin is adhered to the core body 21. Even if the swelling part at the edge part of the resin layer 12a is cut in round slice in the peripheral direction, the edge part after cutting apparently swells similarly.
The cylindrical metal mold 13 and the core supporting members 14, 14 have tolerances of respective parts and assembling spaces, and so-called parting lines occur. If the spaces become large owing to such as abrasion in the respective parts when setting up the metal mold, the resin flows into the spaces and burrs are created at the edges of the resin layer 12a as shown in FIG. 33.
The corner 74 of the resin roller 10a is obtained by forming the surface layer 12b around the resin layer 12a of the resin roller 10a in the above mentioned method, and as shown in FIG. 34, actually the film thickness of a resin forming the surface layer 12b is small.
When the resin roller 10a contacts and slides with the image carrier as the sensitive substance, since the corner of the resin roller 10a contacts the periphery of the image carrier at larger force than that exerting in the center part of the resin roller 10a and the film thickness of the surface layer 13b is smaller than that in the center part, the surface layer 12b of the corner of the resin roller 10a is easily worn, and in turn this abrasion causes the surface layer 12b to peel off, and as a time passes, the surface layer 12b gradually widens to peel in the surface of the resin roller 10a. 
For resolving those occasions, there is a method of uniformly machining or polishing the surface of the resin roller prior to coating the surface layer, but it takes many processing steps, and besides the resin layer is soft, and in particular the corner could not be precisely machined or polished.
Another method is to machine or polish the only corner, but some of elastic resins such as, above all, silicone forming the resin layer have viscosity or stickiness particular to these resins, so that processing parts are nappy or ragged, and the surface cannot be processed to be smooth. There is another available method which carries out the process of immersing or coating water or oil to the processing part of the resin roller while machining or polishing, but after processing, it is further necessary to remove water or oil.
Next, an apparatus of producing the roller will be explained in detail. The apparatus of producing the roller is mainly structured with, as shown in FIG. 35, for example, a cylindrical metal mold 61 and the core supporting members 62a, 62a located at upper and lower both edges of the cylindrical metal mold 61 for supporting a core 21 inserted inside of the cylindrical metal mold 61 and sealing both edges of the cylindrical metal mold 61.
The lower core supporting member 62b is defined with a straight resin injecting inlet 64 for injecting the resin material into a roller forming space 63 formed within the cylindrical metal mold, while the resin injecting inlet is provided on the way with a closure mechanism 68 for regulating a resin fluid. If a resin injecting nozzle (not shown) at the side of the forming machine is urged to a nozzle touch portion 65 formed to be semi-circular with a part opening toward outside of the metal mold of a resin injecting inlet 64, so that the resin material is introduced into the roller forming space 63.
On the other hand, the upper core supporting member 62a is defined with a straight air vent hole 66, and a closure mechanism 67 is provided as crossing with the air vent hole 66 for closing the resin fluid.
The summary of the method of forming the roller by use of this producing apparatus is as follows.
At first, the core body 21 inserted within the cylindrical metal mold 61 is held at its upper and lower edges by the upper and lower core supporting members 62a, 62b, and subsequently a hot-setting liquid resin is filled into the roller forming space 63 through the resin injecting inlet 64, and on completion of filling, the closure mechanism 68 in the lower core supporting member 62b is operated to check a counter flow of the resin expanding within the cylindrical metal mold when hot-setting.
In contrast, the air vent hole 66 provided in the upper core supporting member 62a releases the closure mechanism 67 during filling the resin to exhaust the air in the roller forming space via the air vent hole 66 outside of the metal mold, and on completion of filling the resin, the closure mechanism is closed, and under this condition, the resin staying in the roller forming space is hot-set.
On completion of hardening the resin, the core supporting members 62a, 62b are removed upward and downward from the cylindrical metal mold 61 along the axial direction, and finally a formed product held within the cylindrical metal mold 61 is taken out by extruding the core body 21 with respect to the cylindrical metal mold 61. This is a method of producing rollers by means of this kind of the conventional apparatus.
However, the conventional roller producing apparatus and method are involved with many problems.
For example, in the conventional roller producing method, a metal mold device composed of the core supporting member and the cylindrical metal mold is charged with a thermosetting resin, and then the upper and lower closure mechanisms are closed to make the forming space a closed space. The closed space is filled with the thermosetting resin to form an elastic layer (formed body), and at this time the resin hot-set within the closed metal mold is generated with cubical expansion. Since the filled thermosetting liquid resin is non-compressive, an internal pressure within the metal mold by the cubic expanded resin is considerably high. A magnification of this internal pressure is normally more than 100 kg/cm2, though depending on air tightness of the closure mechanism provided in the core supporting member, and so the metal mold must have sufficient pressure resistant strength. Accordingly, thickness of the cylindrical metal mold is large, and load should be large for connecting the cylindrical metal mold and the core supporting member.
If the internal pressure within the metal mold is large, the resin flows into the parting line between the cylindrical metal mold and core supporting member, and this becomes a burr appearing at the roller peripheral part, so that a secondary process as a polishing is necessary to remove burrs. Further, the resin often leaks from the closure mechanism 68 provided in the lower core supporting member 62b, so that a work is demanded to remove the resin adhered to the metal mold after having formed to cause the working efficiency to go down.
A problem is present when taking out the formed product from the metal mold. If the internal pressure within the metal mold is large, as the surface of the elastic layer is closely adhered to the inner surface of the metal mold, when releasing from the mold after completion of hardening, resistance against releasing from the mold is still large even if the elastic layer is shrunk with enough cooling time, and scratches often appear on the surface of the elastic layer by releasing from the mold. For avoiding these occasions, the cylindrical metal mold is carried out with a fluorine coating treatment, or a plating treatment for heightening smoothness, but with such only measures, the mold releasing property is not yet sufficient, and actually a mold releasing agent is coated on the inside of the metal mold per each time.
Next, referring to FIG. 36, explanation will be made to another conventional method of making rollers using the thermosetting liquid resin. This method comprises mixing silicone-based liquid base polymer (main agent), a cross linking agent, a catalyst and if necessary an electrically conductive agent within a vacuum agitating-defoaming device, rendering this to be one liquid state, storing it in a container 81, subsequently transferring a thermosetting liquid resin 82 in the container 81 by use of a force feed pump 83 to an injection device 84, sending to a cylinder 86, measuring a predetermined amount, and injecting into a cavity of a roller forming metal mold 88 via an injecting nozzle 87, thereby to form a roller main body. Herein, a cooling device 90 is necessary to normally keep cooled at about 10° C. or lower the transferring course comprising the container 81, injecting device 84, injecting nozzle 87 and transferring tube 89. In the illustrated example, a cooling liquid is circulated and supplied from the cooling device 90 through pipes 91a, 91b, 91c, 91d so as to cool each of the parts. The cooling device is provided because if this is absent, a bridging reaction of the thermosetting liquid resin progresses, and the liquid resin is adhered to and solidified on the inner walls of the transferring course comprising the container 81, injecting device 84 and transferring tube 89, and obstacles transferring of the liquid resin, so that the apparatus is frequently necessarily disassembled to clean to remarkably decrease productivity.
Since this cooling system heightens production cost, there is an attempt of adding a hardening retard agent to the liquid resin for avoiding the cost-up, and lengthening a pot life, but as a progressing risk of the bridging reaction of the liquid resin staying in the container 81 is high, a problem occurs in variation of quality between rollers at a beginning period of and after the injection forming.
However, in the conventional roller producing method employing the above mentioned cooling system,    (1) since the thermosetting liquid resin is cooled down at about 10° C. or lower and increases viscosity, an injecting pressure is heightened to fill it into the cavity, it is necessary to design the thickness of the roller forming metal mold to be durable against the injecting pressure, and    (2) if injecting the once cooled liquid resin, a problem arises that a heating load is increased when hot-setting, and a hardening reaction time is extended.
FIG. 37 is a schematically cross sectional view showing another example of the conventional injection forming apparatus (metal mold). In the same, reference numeral 41 designates the cylindrical metal mold, 42 shows the core body inserted inside of the cylindrical metal mold 41, 43, 44 are the core supporting members, 45, 46 are cover members screwed inside with thread, and 47 is a pin. A sequence of forming the elastic roller by use of the injection forming metal mold is as follows. At first, the cylindrical metal mold 41 is inserted with the core body 42, both edge parts 42a, 42b thereof are fitted in core supporting holes 43a, 44a provided in the cylindrical metal molds 43, 44, these core supporting members 43, 44 are engaged in the cylindrical metal mold 41, subsequently screwing cover members 45, 46 on the cylindrical metal mold 41 to protect them and to form the roller forming space 48 for closing the injection forming metal mold.
Next, an attaching hole 49 defined in the cover member 46 is attached with the resin injecting nozzle (not shown), the resin material is injected and filled into the roller forming space 48 through the resin injecting inlet 44b penetrating the core supporting member 44, an attaching hole 150 penetrating the cover member 45 is closed with a pin 47 to shut a vent hole 151, and the cylindrical metal mold 41 is heated to hot-set the resin material. Herein, as the heating means, listed are means contacting a heating mechanism (not shown) to an outside surface of the cylindrical metal mold 41, or means moving the injection forming metal mold into a blast furnace (not shown) to heat it.
After hot-setting, the cylindrical metal mold 41 is cooled, and the metal mold is opened in a sequence reversal to the above mentioned for releasing the formed product from the mold, and by repeating the above mentioned sequence, a new formed product is made.
However, the forming apparatus having the conventional injection forming metal mold as mentioned above has the following problems. One of them is difficult to automatize the steps of fitting the core supporting members 43, 44 in the cylindrical metal mold 41 and mounting the cover members 45, 46 by screwing in the production process, and must depend on manual operation. For example, when screwing the cover members 45, 46 on the cylindrical metal mold 41, if a tightening load is too large, the core body 42 receives excessive load and is easily bent, and if it is too small, the resin material leaks out owing to pressure of the filled resin to generate burrs in a formed product, resulting in decreasing the formability of the roller. Therefore, the tightening load should be adjusted, but automatization of this adjustment is difficult, not depending on the manual operation, and even if the automatization of this kind of steps is possible, since facility investment of the automatized mechanism is very expensive, so that it cannot cope with recent fierce low cost competitions. In particular, in case of mass production using the production apparatus of a plurality of rollers, this problem is remarkable and very much labor is demanded.
In addition, since the prior forming apparatus has such a complicated structure of the metal mold, when getting rid of the adhered and solidified resin after hot-setting, a maintenance working for dissolving and cleaning the roller producing apparatus is troublesome, taking much labor and inviting cost-up.
However, as shown in FIG. 38, when taking out the formed product from the cylindrical metal mold 13 upward or downward along the axial direction, owing to friction between an outer periphery 12e of a resin formed product 12 and an inside 13a of the cylindrical metal mold 13, force is exerted in the axial direction between an outer periphery 21e of the core body 21 and an inside periphery 12f of the resin-formed body 12, and when the formed body is extracted from the cylindrical metal mold 13, a relative position between the core body 21 and the resin-formed body 12 often gets out of position. In particular, force is concentrated to a part X of an edge 12c of the resin-formed body 12 and the core body 21 contacting, and as seen in FIG. 38B, the edge of the resin-formed body 12 and the core body 21 separate, and this portion serves as a trigger to often develop to a whole separation of the resin-formed body 12 and the core body 21. Therefore, a further method is to coat the cylindrical metal mold 13 on the inside with a mold releasing agent for reducing friction between the outer periphery 12e of the resin-formed body of the product and the inside 13a of the cylindrical metal mold, thereby lowering the shifting force exerting in the axial direction between the outer periphery 21e and the inner periphery 12f of the resin-formed body contacting the same. This method increases a step of coating the mold releasing agent, resulting in cost-up.
Silicone based addition type liquid rubber material enabling to be liquid-injected inherently ordinarily used as the resin material for forming the elastic layer; polyether based addition type liquid rubber material which hydrosilyl-hardens terminal allylated polyoxyalkylene based polymer or terminal allylated polyolefin based polymer with poly siloxane based hardening agent; polyolefin based addition type liquid rubber material; urethane based liquid rubber material; EPDM rubber enabling to be injection-formed; millable silicone rubber; or NBR rubber are low in density of polar group contributing to the adhesion or scarcely contain the polar group, thereby to be difficult to adhere a metal made core body. Also in a case of using primer for improving the adhesion of the resin-formed body 12 to the core body 21, depending on the coating of primer to the metal core body 21, influences of adhesion checking substance (for example, a cutting oil) remaining on the metal core body or variation in histories of temperature and moisture after drying, differences arise in a film forming property of the primer component or the adhesion thereof with metal, or residual degree of functional group, so that the adhesion between the resin-formed body 12 and the metal core body 21 might vary. If an injection pressure is high in the metal mold during forming, the primer on the surface of the metal core 21 is forced out by the resin flowing and the primer does not fully display effect, and even if the primer is coated, a sufficiently satisfied adhesion cannot be obtained. Besides, of course a step of coating the primer is added to invite cost-up.
Thus, when taking out the formed product from the cylindrical metal mold 13 upward or downward along the axial direction, owing to friction between an outer periphery 12e of a resin formed product 12 and an inside 13a of the cylindrical metal mold 13, force is exerted in the axial direction between an outer periphery 21e of the core body 21 and an inside periphery 12f of the resin-formed body 12, and a relative position between the core body 21 and the resin-formed body 12 often gets out of position. There is a method of in advance coating the primer to the core 21 for heightening the adhesive strength between the core 21 and the resin-formed body 12, but this method is involved with problems of increasing a primer coating step and that the liquid rubber material used as a resin forming material is inherently weak in the adhesive force with the metal core 21. Therefore, by decrease in the rate of good products by getting out of a relative position between the core 21 and the resin-formed body 12 or addition of the primer coating step, the cost-up is caused in the production of resin rollers.
Accordingly, it is an object of the invention to offer a resin roller enabling to check resin leakage from a formed roller, though using a core body having the same outer diameter in the edge portion as a center part thereof.
It is another object of the invention to offer a resin roller improving durability in a surface layer and in turn having a long life.
It is a further object of the invention to offer a roller producing apparatus which is easy to release from a mold, obtains rollers without scratches or burrs, enables to use a metal mold having a structure of thin thickness and light weight and to shorten a cooling time-before releasing the mold, and a method thereof.
It is a still further object of the invention to offer a roller producing apparatus which does not employ a cooling step of a liquid resin being a technical common knowledge in the prior art, restrains heating load and shortens a hardening reaction time for decreasing energy loss, is excellent in productivity and less to vary product quality, and a method thereof.
It is a yet further object of the invention to offer an apparatus of injection-forming rollers which largely reduces manually operating steps, easily accomplishes automatization of opening and closing the metal mold, lighten maintenance work, and enables to make rollers at low cost.
It is another object of the invention to offer a resin roller which enables to prevent peeling in a part contacting the edge faces of the resin-formed body and the core body for checking getting out of a relative position between the resin-formed body and the core body in the formed resin roller, and a forming metal mold therefor.